A critical component in the commercially viable transportation of bulk cargo from one place to another is the efficient unloading and loading of the cargo from and into the vessels, vehicles and other means which are used to transport it (commonly referred to as ‘carriers’). Indeed, the cost of transporting bulk cargo often determines whether or not production of the goods is economically justified. The efficient unloading and loading of bulk cargo is a multifaceted problem. Factors to be considered may include, inter alia, the physical properties of the cargo such as its natural flow rate or angle of repose in the cargo hold, transportable moisture limits, the time taken for cargo loading or unloading, warehousing costs, the energy and fuel required to move the cargo and the required amount of operators to make it work, as well as the cost of the export vessel charter fees.
In the context of apparatus and systems for unloading and loading of vessels offshore, additional challenges are faced due to the fluid environment in which the operations take place and solutions which are simpler and easier to maintain may be more suitable. It will be understood by those skilled in the art that the invention is particularly suitable in relation to transhippers (generally comprising purpose built self-propelled, shallow draft vessels) which may be used in the offshore transferring of cargo to an export ship or ocean going vessel (‘OGV’).
Considerable volumes of bulk cargo may be transported in the cargo hold of a single carrier. For example, a typical OGV is capable of holding between 10,000 and 100,000 metric deadweight tons (‘DWT’). A typical transhipping vessel which may be used to load an OGV offshore, is capable of holding between 2,500 and 30,000 (or more) DWT. The size and scale of the carriers and machinery involved in the transportation of cargo presents its own unique problems. For example, the apparatus used in the unloading or loading operations needs to be sufficiently robust to handle the forces of the immense amount of materials being transported.
In the past, examples of cargo unloading and loading systems have relied on gravity combined with an undulating or curved cargo hold base and under-hold conveyers to unload cargo from a carrier. Such systems are inefficient in that the undulating or curved base of the cargo hold may reduce overall cargo carrying capacity and the location of the conveyers under the hold itself can make access to the conveyers and other parts of the system difficult, thereby increasing maintenance time and costs. Another limitation of these types of unloading and loading systems is the natural flow rate of some cargo, for example magnetite or lead-zinc concentrate, which due to a propensity to agglomerate or coagulate may not be suitable for such systems.
There are other prior art examples of apparatus and systems for unloading and loading cargo. One such example is a ‘cargo scooper’ system which includes at least two conveyers: a first conveyer extends laterally across the breadth of the cargo hold and includes a plurality of scoops for scooping up cargo in the hold; and a second conveyer extends longitudinally along the length of the cargo hold. Both the first and second conveyers are able to be raised and lowered within the hold. The first conveyer is further able to move along the length of the hold so that it can reach the majority of the volume of the hold with its scoops. The first lateral conveyer collects the cargo by its scoops and transfers it to the second longitudinal conveyer, which in turn transfers the cargo to bucket elevators which raise the cargo upwards for relocation outside of the vessel, craft, etc. The conveyers work on the uppermost parts of the cargo first, and are lowered each successive pass of the first conveyer along the length of the hold to progressively remove the cargo until most of it has been removed from the hold.
Another example is a system which incorporates a screw-based mechanism in a boom for transferring cargo from a hold. Screws are located in the arm of a slewing and luffing boom, which is able to be manoeuvred into the reaches of the hold. The screw, by turning, transfers cargo along the length of the boom for relocation outside of the cargo hold.
These systems are not generally used for loading cargo into a hold, as the loading rate is generally too slow to be commercially viable. Instead these screw-based systems are typically used on the shore infrastructure at the ports to unload cargo from OGV holds, however this again is limited to lower throughput speeds.
The cargo scooper and screw-based prior art systems described above have numerous drawbacks, including high maintenance and running costs. More specifically, the cargo scooping system can be costly to maintain due to the propensity for the cargo scoops or the transverse conveyer to break or otherwise malfunction due to the repetitive heavy forces impacting the apparatus as it scoops cargo directly from the hold. Other disadvantages to the cargo scooping system include substantial operational expenditures due to the numerous moving parts. The screw-based system is hampered by the limited reach of the conventional boom, which may be unable to access all regions of deeper or larger holds. If multiple booms are used to achieve better access to the larger and deeper holds, the system becomes considerably more expensive. Such systems may be hindered by low transfer rates as a result of the limited effective size, length and operating speed of the screws.
Prior art systems, such as those for unloading cargo described above, are generally not capable of delivering efficiencies in both loading and unloading operations.
Furthermore, as previously mentioned, the running and maintenance costs of unloading and loading systems for sea transport of cargo are particularly important in the commercial viability of commodity producers and transporters. Simpler systems which are less prone to malfunction are therefore highly sought after.
In view of the shortcomings of the prior art, as well as the need for more efficient cargo loading and unloading apparatus and systems, it would therefore be desirable to have an apparatus and system for unloading cargo which is relatively simple in design and/or has relatively lower initial capital expenditure and/or lower maintenance and operation costs.
It would also be desirable for the apparatus and/or system to offer advantages in both the unloading and loading operations.
An object of the present invention is to provide a cargo scraping apparatus and/or systems which improve over the prior art, or which at least provide a useful alternative.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.